A system for implanting a wire antenna in a contactless smart card includes an ultrasonic implanting head with a voice-coil actuator to control the pressure at which a heated wire is forced into a plastic card substrate. The force produced by the actuator is proportional to the current in a coil winding in the actuator. A controller uses a feedback system to maintain a relatively constant applied pressure. The feedback system monitors the current in the coil and the controller issues electronic signals to increase or decrease the current in the coil in response to the monitored current.